We have characterized the temperature dependence and calcium dependence of tubulin from sea urchin spindles in previous work. Preliminary studies of whole egg tubulin and tubulin left in the egg after removal of spindles suggest that these species are not different from spindle tubulin. This work must be completed and extended. In addition, tubulin from clam eggs and spindles possesses a high molecular weight protein which cycles with it which is not present in sea urchin tubulin. We will thoroughly characterize all of these tubulins. The work so far suggests that the specificity of where tubulin assembles and how much is present in the cell in microtubule form does not depend on modifications of the tubulin itself but depends upon non-tubulin centers and inhibitors. We have evidence in sea urchins for the presence of protein inhibitors of polymerization and will continue characterizing them. We have discovered two new fibers in the isolated spindle of sea urchin eggs. One is 30-40 A in diameter and is highly concentrated in the centrosomal region but can be found as far out along microtubules as the chromosomes. This material has been found in clam spindles. A second fiber type is variable in thickness (80-120 A) and stretches from membrane to membrane and membrane to microtubule. We will attempt to isolate the thin filament material and characterize it in vitro. We will also raise antibodies to it, study its localization and look for it in other cells. The membrane-membrane connective will be more difficult to characterize, but it is removable from the spindle with neutral detergent and we will attempt to characterize it from such solutions. We will continue work on the development of contractile furrow models of eggs varying glycerination procedures, buffers, etc. in the attempt to develop a consistent cleavage furrow model.